DRV3201-Q1_16 Datasheet, PDF (42/60 Pages) Texas Instruments – DRV3201-Q1 3 Phase Motor Driver-IC for Automotive Safety Applications

DRV3201-Q1
SLVSBD6D – MAY 2012 – REVISED AUGUST 2015
Typical Application (continued)
For steady state, the current in the coil looks like Figure 16.
IL
ILcurlim =
0.1V / Rboost_shunt
Nominal battery
voltage at VS
Iton =
VS*ton
/L
High battery
voltage at VS
Itoff =
(VBOOST-VS)*toff / L
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Low battery
voltage at VS
ton
toff =
VS / (VBOOST * fBOOST)
ton
toff =
VS / (VBOOST * fBOOST)
ton
toff =
VS / (VBOOST * fBOOST)
ton+toff = 1 / fBOOST
ton+toff = 1 / fBOOST
ton+toff = 1 / fBOOST
Figure 16. Coil Current Waveforms in Steady State for Nominal, High and Low Battery Voltage
From this figure, the ripple current and the boost output current can be calculated as follows:
IL_ripple
=
L
g
VS
f_BOOST
g
æç_1-
è
VS
V_BOOST
ö
÷
ø
=
(V_BOOST - VS) g VS
L g f_BOOST g V_BOOST
(5)
I_BOOST
=
VS
V_BOOST
g
IL_curlim
-
1
2
g
æ
ç
(V_BOOST
-
VS)
g
VS
è ^{L g f}BOOST ^{g V}BOOST
ö
÷
ø
(6)
f_BOOST
= 2.5
MHz;
(V_BOOST
- VS)
= 15
V;
IL_{cur lim}
=
æ
ççè
0.1 V
R_{shunt _ boost}
ö
÷÷ø
(7)
As can be seen from Equation 6, the boost output current capability for a given IL_curlim is the lowest for the
minimum supply voltage VS. The boost output current capability should be dimensioned (by setting IL_curlim
with external Rshunt_boost) so the needed output current (based on PWM frequency and gate-charge of the
external power FETs) can be delivered at the needed minimum supply voltage for the application. The following
equation gives IL_curlim as a function of IBOOST and VS:
IL_{cur lim} = I_BOOST g
V_BOOST
VS
+ 1/2
g
æ
ç
V_BOOST
- VS ö
÷
è ^{L g f}BOOST ø
(8)
To set the IL_curlim, the minimum application supply should be used in this equation and IBOOST according to
Equation 3.The minimum application supply voltage the DRV3201-Q1 can support is 4.75 V.
As shown in Equation 6, the boost output current capability increases for higher supply voltage VS. If the boost
output current capability is dimensioned so it can deliver the necessary output current for the minimum supply
voltage, it actually delivers more current than needed for nominal supply voltage and the boost voltage increases.
Therefore, a hysteretic comparator (low level VBOOST-VS = 14 V, high level VBOOST-VS = 16 V) determines
starting/stopping the burst pulsing as shown in Figure 17.
The nominal switching frequency during the burst pulsing is 2.5 MHz once the boost has reached steady state.
During start-up of the boost, the internal time reference is slower by a factor of three, resulting in three times
longer off-times to allow the coil current to decrease sufficiently compared to Equation 4.
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